1. Field of the invention
The present invention relates to a novel 5-O-.alpha.-D-glucopyranosyl-L-ascorbic acid and its biochemical synthesis, as well as to food products such as beverages, processed foods, tobaccos and cigarettes; agents of anti-susceptive diseases such as preventive and/or therapeutic agents for susceptive diseases; and cosmetics such as skin-refining agents and skin-whitening agents.
2. Description of the prior art
L-Ascorbic acid, which has the chemical structure shown by the formula 1: ##STR1## is not synthesized in vivo in human, monkey and guinea pig, therefore it is listed as an essential nutritive element, i.e. vitamin C.
L-Ascorbic acid takes part in some physiological activities in vivo; for example, in the hydroxylation of proline and lysine which are necessary to synthesize collagen as the main element of living connective tissues; the oxidation-reduction reaction of cytochrome C wherein Fe.sup.+++ is reduced to Fe.sup.++ ; and the immunopotentiation via the increase of leukocyte. These are because vitamin C plays a significant role in the maintenance and promotion of health in living body.
Scurvy has been known long as a condition due to deficiency of L-ascorbic acid, and is marked by weakness of the skin, petechial hemorrhage, ecchymosis, and hemorrhages in the gingiva and marrow. To prevent scurvy for the maintenance of health, a recommended daily administration (RDA) is established for L-ascorbic acid; in particular, 60 mg for adult male and 50 mg for adult female.
Nowadays the use of L-ascorbic acid is not limited to agents which enrich vitamin C as an essential nutritive element, but is extending in various applications. More particularly, because of the chemical structure and physiological activities, L-ascorbic acid is useful as a souring agent, reductant, antioxidant, bleaching agent and stabilizer in various chemical reagents, foods and beverages, pharmaceuticals for susceptive diseases such as preventive and remedy for viral diseases, bacterial diseases and malignant tumors; and further as a reductant, uv-absorbent and melanin-formation inhibitor in cosmetics including skin-refining agent and skin-whitening agent.
The major drawback of L-ascorbic acid is that it readily looses the physiological activities because of its poor stability and high susceptibility to oxidation.
To stabilize L-ascorbic acid, some saccharide derivatives of L-ascorbic acid have been proposed.
For example, a biochemical synthesis of L-ascorbic acid glucosides is disclosed in Vitamin, Vol.43, pp.205-209 (1971); ibid., Vol.47, pp.259-267 (1973); and Japanese Patent Publication No.38,158/73.
Because of the facts that (i) the glucosides are prepared by similar methods, (ii) "the formation of an ether bond at the primary alcohol group, which is located at the number six carbon atom in L-ascorbic acid, leads to the glucosides" as described in the Japanese Patent Publication, for example, on the 2nd column, lines 14-16, (iii) the saccharide-transfer reaction from maltose to an .alpha.-glucosyl group is responsible for the formation of glucosides, and (iv) the glucosides exhibit a direct reducing activity; the chemical structure of the glucosides would be shown by the formula 2: ##STR2##
As obvious from the results in the Japanese Patent Publication, i.e. the table in Example 1, the stability of the glucosides is superior to that of L-ascorbic acid, but the level is not enough, and the glucosides can not sufficiently exert a physiological activity because they are substantially not assimilated by the digestive enzyme, and these render the commericialization of the glucosides difficult.
Japanese Patent Laid-Open Nos. 135,992/91 and 139,288/91 disclose that 2-O-.alpha.-D-glucopyranosyl-L-ascorbic acid as shown in formula 3 can be formed by a biochemical synthesis. Formula 3: ##STR3##
The derivative of L-ascorbic acid, however, has a drawback that it could not be used for uses wherein the inherent direct reducing activity of L-ascorbic acid is required.
While Japanese Patent Publication No.5,920/83 discloses an organic chemical process to synthesize saccharide derivatives of L-ascorbic acid.
These saccharide derivatives are, however, those wherein all the D-glucoses are bound in the .beta.-fashion because up to 21 .beta.-D-glucopyranosyl type derivatives of L-ascorbic acid including 2,3-di-O-(.beta.-D-glucopyranosyl)-L-ascorbic acid are listed for explanation on the 7th column, line 6 to the 8th column, line 11.
Japanese Patent Laid-Open No.198,498/83 discloses an organic chemical process to synthesize saccharide derivatives of L-ascorbic acid which are also of .beta.-glucosyl type.
Studies on the .beta.-D-glucopyranosyl type derivatives of L-ascorbic acid confirmed that they hardly exhibit desired physiological activities in a living body, especially, in human.
Furthermore, conventional organic chemical processes have the drawbacks that they are inferior in economical efficiency because the reaction is very complicated and low in yield, as well as that the establishment of non-toxicity and safeness for the resultant derivatives is very difficult.
As described above, the proposals of saccharide derivatives of L-ascorbic acid in the prior art have proved unsatisfactory in view of stability, reducing activity, safeness, physiological activity and economical efficiency, and not been practiced hitherto.
It has been a great demand to realize a derivative of L-ascorbic acid which improves the drawbacks of conventional saccharide derivatives of L-ascorbic acid, as well as having a satisfiable stability, exhibiting a reducing activity, exerting the inherent physiological activity of L-ascorbic acid in vivo, and being used without fear of causing side effects.